#include <iostream>
#include <string>
using namespace std;
int main(){
	ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
	string s;
	int n;
	char c;
	cin >> n;
	cin >> s;
	cin >> c;
	int ans = -1;
	for(int i = 0 ; i < n ; i++){
		if(s[i] == c){
			ans = i;
			break;
		}
	}
	cout << ans;
	return 0;
}